Method for determining key parameters of single-layer braced Larsen steel sheet pile support

Abstract

The present invention proposes a method for determining key parameters of single-layer braced Larsen steel sheet pile support, which relates to the technical field of foundation pit support in water conservancy projects. The key parameters of steel sheet pile support are determined by clarifying the characteristics of the support project, determining the safety level of the foundation pit, calculating the soil pressure and the position of the action point, determining the length of the steel sheet pile, determining the outer diameter and wall thickness of the steel pipe brace, etc. The steps are clear, which not only weakens the reliance on engineering experience, but also reduces the workload of trial calculations, making the calculation results safe and economical, and the calculation process is concise and efficient. It can fully meet the design requirements of double-row steel sheet pile support scenarios for small and medium-sized hydraulic structures, and has broad promotion value.

Description

Technical Field

[0001] The invention relates to the technical field of foundation pit support in water conservancy projects, and in particular to a method for determining key parameters of single-layer braced Larsen steel sheet pile support. Background Art

[0002] In foundation pit support projects, Larsen steel sheet piles are widely used in various projects due to their unique locking design, high strength and durability. At present, when designing steel sheet pile support structures, most projects use traditional assumptions to determine the design scheme.

[0003] The traditional assumption method first preliminarily estimates the embedded depth of the steel sheet pile, the outer diameter of the steel pipe support and the wall thickness based on similar engineering experience, and then verifies them using the stability calculation formula, slenderness ratio and compressive strength formula. If the preliminarily estimated parameters do not meet the requirements of the specification, the parameters need to be re-determined and verified again. This method relies heavily on engineering experience. If the preliminarily estimated parameters are not appropriate, the design calculation work needs to be re-conducted. In addition, the process of increasing the design parameters is subjective. If the increase is too large, it will lead to excessive safety margins in the project, increase the project volume and investment; if the increase is too small, it will require repeated calculations, which is inefficient.

[0004] Although the traditional assumption method can determine the parameters of the engineering support scheme, it cannot directly determine the key design parameters such as the length of the steel sheet pile and the characteristics of the steel pipe based on the known engineering conditions. When the horizontal distance of construction is limited (the horizontal distance of construction is ≤10M), the excavation depth of the foundation pit is limited (the retaining depth of the steel sheet pile is ≤8M), and it is necessary to construct small and medium-sized hydraulic structures such as culverts, underground pipes, and inverted siphons between two steel sheet pile supports, a layer of steel pipe bracing is usually set to control the deformation and bending moment of the steel sheet piles. However, there is still no effective method to directly determine the key design parameters of the steel sheet pile support. The reliability of the support scheme is mainly verified by the traditional assumption method. Not only are the final design parameters often not economical, resulting in a waste of engineering resources and an increase in engineering investment costs, but also the work steps are repeated and the workload is huge.

[0005] Therefore, it is of great significance to provide a method that can narrow the parameter range and clarify the calculation steps to improve engineering economy and design efficiency. Summary of the invention

[0006] The present invention aims to solve the problems of poor economy and low efficiency in determining the key design parameters of single-layer braced Larsen steel sheet pile support in the prior art. After clarifying the engineering characteristics (such as steel sheet pile retaining depth, soil properties, etc.), the key design parameters of the single-layer steel pipe braced steel sheet pile support structure can be quickly and accurately obtained, including the length of the steel sheet pile, the outer diameter and wall thickness of the steel pipe brace, etc., thereby simplifying the steel sheet pile support design process, effectively saving engineering resources, and reducing engineering investment costs.

[0007] To achieve the above object, the present invention provides a method for determining key parameters of single-layer braced Larsen steel sheet pile support, comprising the following steps:

[0008] S1: Clarify the engineering characteristics and determine the retaining depth of the foundation pit H ;

[0009] S2: According to the geotechnical engineering condition category, surrounding environmental impact coefficient α and foundation pit excavation depth H , the foundation pit safety level is divided into level one, level two or level three;

[0010] S3: 1.3 times the retaining depth H As a benchmark, select the common pile length that is closest to and greater than the benchmark length as the initial proposed pile length. L ， Based on the initial pile length L Calculate the standard value of the combined active earth pressure E outside the steel sheet pile ak Its action point location , and the standard value of the internal passive earth pressure E pk Its action point location ;

[0011] S4: Verify the pile length using the embedment stability formula and the anti-uplift stability formula L Whether stability requirements are met;

[0012] S5: If the pile is long L If the stability requirements are not met, the pile length is adjusted in 3M increments and re-verified until the requirements are met or the solution is determined to be inapplicable;

[0013] S6: Select outer diameter For a circular steel pipe with a length of 0.273m, calculate the minimum wall thickness of the circular steel pipe to meet the slenderness ratio λ≤150;

[0014] S7: Use the compressive strength formula to verify whether the wall thickness of the steel pipe brace meets the design requirements. If the wall thickness of the steel pipe brace does not meet the compressive strength requirements, select a larger wall thickness from the common steel pipe brace wall thicknesses and return to S6 to recalculate whether the slenderness ratio requirements are met. After the slenderness ratio requirements are met, compressive strength verification is performed again until the design requirements are met.

[0015] In one embodiment, the basis for dividing the foundation pit safety level in S2 is:

[0016] When the foundation pit safety level is level one, the embedded stability safety factor K e =1.25, anti-uplift safety factor K b =1.8;

[0017] When the foundation pit safety level is level 2, the embedded stability safety factor K e =1.2, anti-uplift safety factor K b =1.6;

[0018] When the foundation pit safety level is level three, the embedded stability safety factor K e =1.15, anti-uplift safety factor K b =1.4.

[0019] In one embodiment, the common pile length in S3 is 6m, 9m, 12m, 15m or 18m, and the initial pile length L Need to meet L ≥1.3H.

[0020] In one embodiment, the embedding stability formula in S4 is:

[0021]

[0022] Among them, α is the distance between the brace and the top of the steel sheet pile, and the common value range in engineering is 1 to 2m.

[0023] In one embodiment, the anti-uplift stability formula in S4 is:

[0024]

[0025] Where Y m1 , Y m2 They are the natural weight of the soil above the bottom of the steel sheet pile on the outside and inside of the steel sheet pile (KN / m 3 ); For multi-layer soil, take the average weight of each layer weighted by thickness;

[0026] N c 、N q is the bearing capacity coefficient;

[0027] q 0 is the uniformly distributed load on the ground (kPα);

[0028] , are the cohesion (kPα) and internal friction angle (°) of the soil below the bottom of the steel sheet pile.

[0029] is the natural density of the i-th layer of soil outside the steel sheet pile (kN / m 3 );

[0030] is the natural density of the i-th layer of soil inside the steel sheet pile (kN / m 3 );

[0031] is the thickness of the i-th layer of soil outside the steel sheet pile (m);

[0032] is the thickness of the i-th layer of soil inside the steel sheet pile (m);

[0033] is the number of soil layers outside the steel sheet pile;

[0034] It is the number of soil layers inside the steel sheet pile.

[0035] In one embodiment, the wall thickness of the circular steel tube in S6 is determined by the following formula:

[0036]

[0037] In the formula, μ is the length factor, which is 1;

[0038] A is the cross-sectional area of ​​the circular steel pipe (m 2 );

[0039] t is the wall thickness of the circular steel pipe (m);

[0040] I is the moment of inertia of the circular steel tube section (m 4 );

[0041] r is the radius of gyration of the circular steel tube section (m);

[0042] λ is the slenderness ratio of the circular steel tube;

[0043] D is the length of the steel pipe, that is, the construction distance between two steel sheet piles (m).

[0044] In one embodiment, the compressive strength formula in S7 is:

[0045]

[0046] In the formula, is the plane spacing of the braces (m);

[0047] is the compressive strength of circular steel pipe (MPα);

[0048] f is the design value of steel compressive strength (MPα).

[0049] In one embodiment, the method further comprises step S8: generating a support structure design parameter report including pile length L , outer diameter of steel pipe = 0.273m, steel pipe wall thickness t and corresponding stability verification results.

[0050] The beneficial effects of the present invention are:

[0051] 1. The present invention can accurately determine the minimum parameter value that meets the engineering safety requirements through scientific and reasonable calculations and parameter range limitations. When determining the length of the steel sheet pile, through strict calculations of the embedding depth and the stability of the pit bottom bulge, it is ensured that the pile length can both ensure the safety of the foundation pit and not be too long to cause waste of steel; when selecting the wall thickness of the steel pipe support, first calculate the wall thickness that meets the slenderness ratio requirements, and then combine the compressive strength verification to select the minimum wall thickness that just meets the requirements, avoiding material waste caused by excessive wall thickness and effectively realizing the saving of engineering resources.

[0052] 2. The present invention directly calculates and determines key design parameters by clear and definite steps, based on engineering characteristics, using specific formulas and standards. When determining the length of the steel sheet pile, according to the Technical Regulations for Construction Foundation Pit Support, from 1.3 H We started by considering the initial value and quickly locked in the preliminary pile length in combination with the common pile lengths. Then, through precise soil pressure calculations and stability judgments, we gradually optimized the pile length, thus avoiding repeated trial calculations caused by the assumed pile length in the traditional method. This greatly shortened the design cycle, significantly improved design efficiency, and enabled the project to enter the implementation stage more quickly.

[0053] 3. In the process of determining key parameters, the present invention comprehensively considers many factors that affect the stability of foundation pit support. When determining the safety level of the foundation pit, the geotechnical engineering condition category and the surrounding environmental impact coefficient are fully considered to ensure that the safety level division is accurate and reasonable; when calculating the soil pressure, different calculation formulas are used according to the characteristics of different soil layers and groundwater conditions to accurately calculate the active soil pressure and passive soil pressure; when determining the pile length, the double verification of the embedding depth and the stability of the pit bottom bulge ensures that the steel sheet pile can stably and safely complete the support work under various working conditions.

[0054] This multi-factor comprehensive design method improves the efficiency of engineering resource utilization, ensures the safety and reliability of the support scheme, protects the lives of construction workers and the safety and stability of surrounding buildings, and shortens the design cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Determine the workflow diagram for the key parameters of the present invention.

[0056] Figure 2 It is a schematic diagram of the construction of single-layer circular steel pipe braced steel sheet pile support according to the present invention. DETAILED DESCRIPTION

[0057] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0058] S1: Clarify the engineering characteristics and determine the retaining depth of the foundation pit H .

[0059] Taking a city culvert construction project as an example, it is necessary to excavate a foundation pit in a narrow construction area (horizontal distance is 8m), and the retaining depth is H =6m.

[0060] The soil layer distribution and geological conditions are as follows: (1) Surface fill (clay soil, thickness 2m, natural density Y 1 =17 kN / m 3 , c 1 =10MPα, =15°); (2) Lower clay layer (thickness 4m, saturated density =20 kN / m 3 , natural density =19kN / m 3 , c 2 =15kPα, =25°); (3) Deep clay (thickness 5m, saturated density =20 kN / m 3 , c 3 =25MPα, =25°). The groundwater level is 3m below the ground surface.

[0061] Surrounding environment: The edge of the foundation of the adjacent old building is 4m away from the foundation pit, and the foundation is buried 2m deep. Consider the additional load evenly distributed on the ground. The surrounding environmental impact coefficient α is the ratio of the horizontal distance from the outer edge of the foundation of the adjacent buildings and structures around the foundation pit to the edge of the foundation pit bottom to the vertical distance from the bottom surface of the foundation of the outer edge of the foundation of the building and structure to the bottom of the foundation pit. Therefore, in this embodiment, α=4 / (6-2)=1.0;

[0062] Material of the bracing steel pipe: Q235 (design value of compressive strength f=215MPα).

[0063] S2: According to the geotechnical engineering condition category, the surrounding environmental impact coefficient α and the foundation pit excavation depth h, the foundation pit safety level is divided into level one, level two or level three. Determine the foundation pit safety level according to the following table:

[0064]

[0065] Note: When α≤1.0 and there are important buildings, structures, pipelines or lifeline projects, the foundation pit safety level should be level one.

[0066] In this project, the geotechnical engineering condition category is Class II, the surrounding environmental impact coefficient α=1.0, and the foundation pit excavation depth h=H=6m 。 Therefore, the safety level of the foundation pit is Level 2. e =1.2、 K b =1.6 。

[0067] S3: 1.3 times the retaining depth H As a benchmark, select the common pile length that is closest to and greater than the benchmark length as the initial proposed pile length. L ， Based on the initial pile length L Calculate the standard value of the combined active earth pressure E outside the steel sheet pile ak Its action point location , and the standard value of the internal passive earth pressure E pk Its action point location .

[0068] Reference pile length L =1.3H=1.3×6=7.8m;

[0069] Steel sheet piles are prefabricated parts. Common pile lengths are 6m, 9m, 12m, 15m or 18m. The closest common pile length here is 9m, so the initial proposed pile length is L Select 9m.

[0070] 1. Active earth pressure calculation:

[0071] (1) Fill layer (0-2m, above groundwater level):

[0072] Vertical stress of soil at z=2m: (z is the depth from the ground, the same below);

[0073] Active earth pressure coefficient: ;

[0074] Active earth pressure strength of soil at z=2m:

[0075] .

[0076] (2) Lower clay layer (2-6 m):

[0077] ①2~3m (above groundwater level):

[0078] Vertical stress of soil at z=3m:

[0079] ;

[0080] Active earth pressure coefficient: ;

[0081] Active earth pressure strength of soil at z=3m:

[0082] .

[0083] ②3~6m (below the groundwater level), considered as the soil layer with good water-soil balance:

[0084] Vertical stress of soil at z=6m:

[0085] ;

[0086] Active earth pressure strength of soil at z=6m:

[0087] .

[0088] (3) Deep clay layer (6-9 m):

[0089] Vertical stress of soil at z=9m:

[0090] ;

[0091] Active earth pressure coefficient:

[0092] Active earth pressure strength of soil at z=9m:

[0093] .

[0094] The resultant force of each layer is calculated by the trapezoidal area integration method. ;in, is the thickness of the i-th layer of soil outside the steel sheet pile ( m );

[0095] Fill layer (0-2m): ;

[0096] Lower clay layer (2-3 m): ;

[0097] Lower clay layer (3-6 m): ;

[0098] Deep clay layer (6-9m): ;

[0099] Total active earth pressure resultant:

[0100] .

[0101] 2. Active action point location calculate:

[0102]

[0103] in, is the distance between the active earth pressure resultant and the pile bottom (m);

[0104] is the distance from the point of action of the active earth pressure resultant of the i-th soil layer to the bottom of the pile (m);

[0105] is the active earth pressure of the i-th soil layer (KN);

[0106] is the active earth pressure resultant (KN).

[0107] Position of action point of single soil layer:

[0108]

[0109] in, is the thickness of the i-th layer of soil outside the steel sheet pile (m);

[0110] is the active earth pressure strength on the top surface of the i-th soil layer ( );

[0111] is the active earth pressure strength at the bottom of the i-th soil layer ( );

[0112] is the total thickness of each layer of soil below the i-th layer of soil outside the steel sheet pile (m);

[0113] It is the number of soil layers below the i-th soil layer outside the steel sheet pile.

[0114] (1) Calculate the distance between the action point of each layer of soil pressure and the pile bottom:

[0115] Fill layer (0-2m): ;

[0116] Lower clay layer (2-3 m): ;

[0117] Lower clay layer (3-6 m): ;

[0118] Deep clay layer (6-9m): ;

[0119] (2) Calculate the position of the total action point:

[0120] ;

[0121] 3. Passive earth pressure calculation:

[0122] Deep clay layer (6-9m), considered as a soil layer with good water-soil balance:

[0123] Vertical stress of soil at z=9m: ;

[0124] Passive earth pressure coefficient: ;

[0125] Passive earth pressure strength of soil at z=9m:

[0126] ;

[0127] Calculate the resultant force by the trapezoidal area integration method, ;in, is the thickness of the i-th layer of soil inside the steel sheet pile (m);

[0128] Deep clay layer (6-9m): .

[0129] 4. Passive action point location calculate:

[0130]

[0131] in, is the distance between the passive earth pressure resultant and the pile bottom (m);

[0132] is the distance from the bottom of the pile to the resultant passive earth pressure of the i-th soil layer (m);

[0133] is the passive earth pressure of the i-th soil layer (kN);

[0134] is the passive earth pressure resultant (kN).

[0135] Position of action point of single soil layer:

[0136]

[0137] in, is the thickness of the i-th soil layer inside the steel sheet pile (m);

[0138] is the passive earth pressure strength on the top surface of the i-th soil layer ( );

[0139] is the passive earth pressure strength at the bottom of the i-th soil layer ( );

[0140] is the total thickness of each layer of soil below the i-th layer of soil inside the steel sheet pile (m);

[0141] w It is the number of soil layers below the i-th soil layer outside the steel sheet pile.

[0142] Deep clay layer (6-9): .

[0143] In summary, , , , .

[0144] S4: Verify whether the pile length L meets the stability requirements through the embedded stability formula and the anti-uplift stability formula.

[0145] 1. Verification of embedded stability:

[0146] α is 1.5m:

[0147]

[0148] Bring in data: ;

[0149] Therefore, the embedment stability meets the requirements.

[0150] 2. Anti-uplift stability verification:

[0151]

[0152] (1) Calculation and :

[0153] Because the soil above the bottom of the outer side of the steel sheet pile includes fill layer and clay layer, so:

[0154]

[0155] The soil above the inner bottom of the steel sheet pile is only deep clay, so:

[0156] 。

[0157] (2) Calculate N q :

[0158] Because the soil below the bottom of the steel sheet pile is still deep clay, the cohesion of the soil is C 3 and internal friction angle They are and 25°, then .

[0159] (3) Calculate N c :

[0160] ;

[0161] Substituting the parameters into the anti-uplift stability formula, we get:

[0162] ;

[0163] Therefore, the anti-uplift stability meets the requirements.

[0164] S5: If the pile length L does not meet the stability requirements, adjust the pile length in 3m increments and re-verify until it is met or the solution is determined to be inapplicable.

[0165] In this embodiment, L=9m, which meets the stability requirements. The pile length L is the key design parameter determined in this embodiment, and there is no need to adjust the pile length. If the stability requirements are not met, the pile lengths of L+3m, L+6m, L+9m... (pile length ≤ 18m) are taken in turn to repeat the above S3 and S4 operations; if it is still not met in the end, it means that the foundation pit retaining height is too large or the engineering geological conditions are poor, and it is not suitable to use steel sheet pile support.

[0166] S6: Select outer diameter For a circular steel pipe with a length of 0.273m, calculate the minimum wall thickness of the circular steel pipe that meets the slenderness ratio λ≤150.

[0167] Outer diameter of steel pipe is 0.273m, and the length of the steel pipe D is 8m (construction distance);

[0168] formula: , where the length factor μ=1;

[0169] The common outer diameter of a round steel pipe is 273mm, and the corresponding common wall thickness has a variety of sizes to choose from, such as 12, 13, 14, 15, 16, 17, 18, 19, 20, 22, 24, 25, 26, 28, 30, 32mm, etc. Here, we measure from small to large until we get the minimum wall thickness that meets the slenderness ratio requirements to save engineering resources. Assume that the initial wall thickness t=12mm, and calculate the cross-sectional characteristics:

[0170] ;

[0171] ;

[0172] ;

[0173] ;

[0174] It can be seen that when the wall thickness of the circular steel pipe is 12 mm, the slenderness ratio requirement is met.

[0175] S7: Use the compressive strength formula to verify whether the wall thickness of the steel pipe brace meets the design requirements. If the wall thickness of the steel pipe brace does not meet the compressive strength requirements, select a larger wall thickness from the common steel pipe brace wall thicknesses and return to S6 to recalculate whether the slenderness ratio requirements are met. After the slenderness ratio requirements are met, compressive strength verification is performed again until the design requirements are met.

[0176] The formula is:

[0177]

[0178] The common bracing spacing is 2m. Take it as 2m;

[0179] ;

[0180] It can be seen that when the wall thickness of the round steel pipe is 12mm, it meets the compressive strength requirements. , wall thickness t is the key design parameter determined in this project.

[0181] S8: Generate a support structure design parameter report, including pile length L, steel pipe outer diameter =0.273m, steel pipe wall thickness t and corresponding stability verification results.

[0182] Steel sheet pile length L=9m ；

[0183] Steel pipe bracing dimensions: 273×12mm;

[0184] Safety factor verification: embedded stability safety factor 2.56, anti-uplift safety factor 6.32, slenderness ratio 86.96, compressive strength 37.58 MPa , all meet the design standards, and the steel sheet pile support scheme can be implemented.

[0185] Compared with the existing technology, assuming that the same project is designed using the traditional assumption method:

[0186] Initial parameters: Based on engineering experience, the pile length L=12mm and the steel pipe 325×16mm;

[0187] Trial calculation process: The pile length and steel pipe size need to be adjusted several times, which takes about 1.5 days;

[0188] Result: L=12mm, Although the 325×16mm steel sheet pile support solution meets the safety requirements, compared with the embodiment of the present invention, when arranging 50m long (single-side) steel sheet pile support, the steel quality used in the method adopted by the present invention is:

[0189]

[0190] The same project adopts the traditional assumption method, and the steel quality is:

[0191] The method adopted by the present invention reduces the steel mass by 33.4%.

[0192] The present invention combines engineering characteristics with a formulaic process method, and the steel mass of the support scheme determined by the present invention is less than that of the traditional assumption method, and the cost is significantly reduced. It realizes the rapid optimization and determination of key support parameters, and at the same time shortens the design time from 1.5 days to 4 hours, thereby improving the engineering economy and design efficiency. It has broad promotion value for the double-row steel sheet pile support scenarios of small and medium-sized hydraulic structures.

[0193] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A method for determining key parameters of single-layer Larsen steel sheet pile support, characterized in that: The following steps are involved: S1: Clarify the engineering characteristics and determine the retaining depth H of the foundation pit; S2: According to the geotechnical engineering condition category, the surrounding environmental impact coefficient α and the excavation depth h of the foundation pit, the foundation pit safety level is divided into level 1, level 2 or level 3; S3: Taking 1.3 times the retaining depth H as the benchmark, select the common pile length that is closest to and greater than the benchmark length as the initial proposed pile length L, and calculate the standard value of the combined active earth pressure E on the outer side of the steel sheet pile based on the initial proposed pile length L. ak and its point of action l 主动 , and the standard value of the internal passive earth pressure E pk and its point of action l 被动 ; S4: Verify whether the pile length L meets the stability requirements through the embedment stability formula and the anti-uplift stability formula; S5: If the pile length L does not meet the stability requirements, adjust the pile length in 3m increments and re-verify until it is met or the solution is determined to be inapplicable; S6: Select outer diameter D 钢管 For a circular steel pipe with a length of 0.273 m, calculate the minimum wall thickness of the circular steel pipe that satisfies the slenderness ratio λ≤150, wherein the minimum wall thickness is selected from common wall thickness sizes; S7: Use the compressive strength formula to verify whether the wall thickness of the steel pipe brace meets the design requirements. If the wall thickness of the steel pipe brace does not meet the compressive strength requirements, select a larger wall thickness from the common steel pipe brace wall thicknesses and return to S6 to recalculate whether the slenderness ratio requirements are met. After the slenderness ratio requirements are met, compressive strength verification is performed again until the design requirements are met.

2. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 1 is characterized in that: The basis for the classification of the foundation pit safety level in S2 is: When the foundation pit safety level is level one, the embedded stability safety factor K e =1.25, anti-uplift safety factor K b =1.8; When the foundation pit safety level is level 2, the embedded stability safety factor K e =1.2, anti-uplift safety factor K b =1.6; When the foundation pit safety level is level three, the embedded stability safety factor K e =1.15, anti-uplift safety factor K b =1.

4.

3. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 1 is characterized in that: The common pile lengths in S3 are 6m, 9m, 12m, 15m or 18m, and the initial proposed pile length L must satisfy L≥1.3H.

4. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 2 is characterized in that: The embedding stability formula in S4 is: Among them, a is the length of the brace from the top of the steel sheet pile, and the common value range in engineering is 1 to 2m.

5. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 2 is characterized in that: The anti-uplift stability formula in S4 is: In the formula, γ m1 , γ m2 The natural weight of the soil above the bottom of the steel sheet pile on the outside and inside of the steel sheet pile (kN / m 3 ) For multi-layer soil, take the average weight of each layer weighted by thickness; N c 、N q is the bearing capacity coefficient; q0 is the uniformly distributed load on the ground (kPa); c. are the cohesion (kPa) and internal friction angle (°) of the soil below the bottom of the steel sheet pile, respectively; γ ak,i is the natural weight of the i-th layer of soil outside the steel sheet pile (kN / m 3 ); γ pk,i is the natural density of the i-th layer of soil inside the steel sheet pile (kN / m 3 ); h ak,i is the thickness of the i-th layer of soil outside the steel sheet pile (m); h pk,i is the thickness of the i-th soil layer inside the steel sheet pile (m); n1 is the number of soil layers outside the steel sheet pile; n2 is the number of soil layers inside the steel sheet pile.

6. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 1 is characterized in that: The wall thickness of the circular steel tube in S6 is determined by the following formula: In the formula, μ is the length factor, which is 1; A is the cross-sectional area of ​​the circular steel pipe (m 2 ); t is the wall thickness of the circular steel pipe (m); I is the moment of inertia of the circular steel tube section (m 4 ); r is the radius of gyration of the circular steel pipe section (m); λ is the slenderness ratio of the circular steel tube; D is the length of the steel pipe, that is, the construction distance between two steel sheet piles (m).

7. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 1 is characterized in that: The compressive strength formula in S7 is: Where, d 对撑 is the plane spacing of the braces (m); σ is the compressive strength of circular steel pipe (MPa); f is the design value of steel compressive strength (MPa).

8. The method for determining key parameters of single-layer braced Larsen steel sheet pile support according to claim 1 is characterized in that: The method further comprises step S8: generating a support structure design parameter report, including pile length L, steel pipe outer diameter D 钢管 =0.273m, steel pipe wall thickness t and corresponding stability verification results.

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